Hello Pinto,
A friend of mine bought a generator and decided to build a cover for it, not just to protect it from the rain but to try and reduce the noise it made. - Bad mistake. Generators not only produce electricity, they produce noise fumes and HEAT. After only a about an hour of use, the generator over heated and the alternator burnt out even though it was working on a fraction of the load it was designed for.
If you only want rain protection, then an umbrella! But I always wonder if caravanners need a generator, virtually all the appliances in the caravan can either be run on 12V dc or use gas.
Just a few facts to consider:-
Unless you have an inverter controlled output generator, the output of most simple load controlled generators is not very stable, and changes in load can cause voltage spikes that can damage many of the electronic systems now found in caravans.
Even the large petrol engined generators are at best only 4 to 6% efficient at converting petrol fuel to usable electrical power, so smaller ones are likely to be only 3 to 5% efficient. By comparison, all the gas burning appliances you have in your caravan have to at least 70% efficient (and in many cases they exceed 80%) so cost for cost using gas in preference to a generator will be substantially cheaper, and kinder to the environment, and your fellow caravanners.
If you really do need 230vac, then for modest loads (eg, up to 300W) you can get an inverter that runs of the 12V battery, but these should be used sparingly.
There are times and places when a generator is the only practical solution, and I do use them at festivals etc, but for normal caravan touring, there are some very real and viable alternatives.